Washington — Stating that the United States is in the highest terrorist threat environment since 9/11, the chairman of the House Homeland Security Committee said Wednesday that America must make a greater effort to reach out to the Muslim community to spot early warning signs of self-radicalization.

In last week’s mass shooting in San Bernardino, Calif., family members had noticed Syed Rizwan Farook’s radicalization, but they didn’t say anything, said Rep. Michael McCaul (R) of Texas. He cited evidence that Mr. Farook and his wife, Tashfeen Malik, were radicalized before 2014, when they got married in the US.

“Signs of radicalization don’t just happen overnight,” he said. In every case he’s studied, from the Boston Marathon bombings to the shootings in Chattanooga, Tenn., to the San Bernardino killings, “the signs are there.”

FBI Director James Comey said Wednesday that the couple was talking about jihad and martyrdom at the end of 2013. They had become radicalized before the rise of the Islamic State, Mr. Comey said.

Self-radicalization, often via the Internet, is one reason that McCaul characterized now as “the highest threat environment since 9/11.” But Europe is at greater risk than America, he said, because it is “far more wide open” to potential terrorists.

Other reasons for the increased danger are the influx of foreign fighters to Syria and Iraq who travel back to their home countries (a factor in the Nov. 13 Paris massacre) and the ability of terrorists to communicate in so-called dark space without detection (also a factor in Paris).

The House this week overwhelmingly passed a bill to tighten up a visa waiver program that allowed passport holders from 38 countries easy entry to the US. The bill has its roots in a bipartisan task force on McCaul’s committee that was set up to look at the foreign-fighter problem.

The chairman is also calling for a national commission to find a “technology solution” to the dark-space problem, which pits intelligence concerns against ones about privacy.

“If you can’t see what the terrorists are saying ... quite honestly, you can’t stop it,” McCaul said Wednesday.

The fight against the Islamic State and the issue of Syrian refugees have taken center stage in the 2016 presidential campaign. When asked about the intense political rhetoric, McCaul warned that it can “inflame the Islamic world” and help with recruiting efforts. He watches the Islamic State videos, he said, and described them as “very sophisticated.”

On Monday, Donald Trump, the lead GOP presidential candidate, called for a temporary ban on all Muslims coming into the US. Republicans and Democrats were swift to criticize the idea. McCaul, a former federal prosecutor, said he did not believe such a ban was constitutional. “We’re founded upon freedom of religion,” he said.

The chairman may have a mild manner about him, but he minced no words in his criticism of Mr. Obama – or the Democratic presidential front-runner and former secretary of State, Hillary Clinton, whom he called the "architect" of the president's foreign policy.

Given Iraq's implosion after the withdrawal of US troops, “she and the president are responsible for ISIS rearing its ugly head,” said McCaul, using an acronym for the Islamic State.

He called for more US Special Operations Forces – not combat troops – to guide airstrikes; a change in the rules of engagement so that more strikes can be carried out; and a no-fly zone in Syria, among other things.

The fight against the Islamic State needs to be given priority, he said: “I don’t think the president has given it the proper attention and priority, because this was not supposed to happen under his watch.”